- Reginald Owen - Dr. Becquerel
- Van Johnson - Reporter
- Margaret O'Brien - Irene Curie - Age 5
- James Hilton - Narration Spoken By (voice)
- Mariska Aldrich - Tall Woman (uncredited)
- Tony Carson - Man at Accident (uncredited)
- Ruth Cherrington - Swedish Queen (uncredited)
- Ray Collins - Lecturer (voice) (uncredited)
- Guy D'Ennery - Professor (uncredited)
- George Davis - Cart Driver (uncredited)
- Harold De Becker - Professor (uncredited)
- Franz Dorfler - Assistant Tailor (uncredited)
- Justine Duney - Woman at Accident (uncredited)
- Tay Dunn - Man at Accident (uncredited)
- William Edmunds - Cart Driver (uncredited)
- Nestor Eristoff - Board Member (uncredited)
- Al Ferguson - Man at Accident (uncredited)
- Edward Fielding - Board Member (uncredited)
- Howard Freeman - Prof. Constant (voice) (uncredited)
- Linda Lee Gates - Perot Granddaughter (uncredited)
- Marie Louise Gates - Perot Granddaughter (uncredited)
- Lisa Golm - Lucille (uncredited)
- Ilka Grüning - Seamstress (uncredited)
- Lumsden Hare - Professor Roget (uncredited)
- Teddy Infuhr - Son (uncredited)
- James Kirkwood - Board Member (uncredited)
- Isabel La Mal - Woman at Accident (uncredited)
- Gene Lockhart - Bit Part (uncredited)
- Miles Mander - Businessman (uncredited)
- George Meader - Singing Professor (uncredited)
- Dickie Meyers - Master Michaud (uncredited)
- Noel Mills - Wedding Guest (uncredited)
- Leo Mostovoy - Photographer (uncredited)
- Alan Napier - Dr. Bladh (uncredited)
- Moroni Olsen - President of Businessman's Board (uncredited)
- María Pagés - Woman at Accident (uncredited)
- Gigi Perreau - Eve at 18 Months (uncredited)
- Francis Pierlot - Monsieur Michaud (uncredited)
- Nita Pike - Woman at Accident (uncredited)
- Dorothy Raye - Nurse (uncredited)
- Almira Sessions - Madame Michaud (uncredited)
- Arthur Shields - Businessman (uncredited)
- Wyndham Standing - King Oscar (uncredited)
- Ray Teal - Driver (uncredited)
- Charles Trowbridge - Board Member (uncredited)
- Michael Visaroff - Proud Papa (uncredited)
- Marek Windheim - Jewelry Salesman (uncredited)
- Frederick Worlock - Businessman (uncredited)
- Eustace Wyatt - Doctor (uncredited)
- Mervyn LeRoy
- Paul Osborn
- Hans Rameau
- Sidney Franklin
- E.J. Mannix
- Herbert Stothart
Greer Garson hace el papel de Marie Curie.
Walter Pidgeon interpreta a Pierre Curie en la película.
Henry Travers interpreta a Eugene Curie en la película.
Albert Bassermann hace el papel de Professor Jean Perot.
Robert Walker interpreta a David Le Gros en la película.
C. Aubrey Smith interpreta a Lord Kelvin en la película.
May Whitty hace el papel de Madame Eugene Curie.
Victor Francen interpreta a President of University en la película.
Elsa Bassermann interpreta a Madame Perot en la película.
Reginald Owen hace el papel de Dr. Becquerel.
Van Johnson hace el papel de Reporter.
Margaret O'Brien interpreta a Irene Curie - Age 5 en la película.
James Hilton interpreta a Narration Spoken By (voice) en la película.
Mariska Aldrich interpreta a Tall Woman (uncredited) en la película.
Tony Carson interpreta a Man at Accident (uncredited) en la película.
Ruth Cherrington interpreta a Swedish Queen (uncredited) en la película.
Ray Collins interpreta a Lecturer (voice) (uncredited) en la película.
Guy D'Ennery interpreta a Professor (uncredited) en la película.
George Davis interpreta a Cart Driver (uncredited) en la película.
Harold De Becker interpreta a Professor (uncredited) en la película.
Franz Dorfler interpreta a Assistant Tailor (uncredited) en la película.
Justine Duney hace el papel de Woman at Accident (uncredited).
Tay Dunn interpreta a Man at Accident (uncredited) en la película.
William Edmunds interpreta a Cart Driver (uncredited) en la película.
Nestor Eristoff hace el papel de Board Member (uncredited).
Al Ferguson hace el papel de Man at Accident (uncredited).
Edward Fielding hace el papel de Board Member (uncredited).
Howard Freeman hace el papel de Prof. Constant (voice) (uncredited).
Linda Lee Gates hace el papel de Perot Granddaughter (uncredited).
Marie Louise Gates interpreta a Perot Granddaughter (uncredited) en la película.
Lisa Golm interpreta a Lucille (uncredited) en la película.
Ilka Grüning interpreta a Seamstress (uncredited) en la película.
Lumsden Hare interpreta a Professor Roget (uncredited) en la película.
Teddy Infuhr interpreta a Son (uncredited) en la película.
James Kirkwood interpreta a Board Member (uncredited) en la película.
Isabel La Mal interpreta a Woman at Accident (uncredited) en la película.
Gene Lockhart interpreta a Bit Part (uncredited) en la película.
Miles Mander interpreta a Businessman (uncredited) en la película.
George Meader hace el papel de Singing Professor (uncredited).
Dickie Meyers interpreta a Master Michaud (uncredited) en la película.
Noel Mills interpreta a Wedding Guest (uncredited) en la película.
Leo Mostovoy interpreta a Photographer (uncredited) en la película.
Alan Napier interpreta a Dr. Bladh (uncredited) en la película.
Moroni Olsen interpreta a President of Businessman's Board (uncredited) en la película.
María Pagés interpreta a Woman at Accident (uncredited) en la película.
Gigi Perreau interpreta a Eve at 18 Months (uncredited) en la película.
Francis Pierlot interpreta a Monsieur Michaud (uncredited) en la película.
Nita Pike interpreta a Woman at Accident (uncredited) en la película.
Dorothy Raye interpreta a Nurse (uncredited) en la película.
Almira Sessions hace el papel de Madame Michaud (uncredited).
Arthur Shields interpreta a Businessman (uncredited) en la película.
Wyndham Standing hace el papel de King Oscar (uncredited).
Ray Teal interpreta a Driver (uncredited) en la película.
Charles Trowbridge interpreta a Board Member (uncredited) en la película.
Michael Visaroff interpreta a Proud Papa (uncredited) en la película.
Marek Windheim interpreta a Jewelry Salesman (uncredited) en la película.
Frederick Worlock interpreta a Businessman (uncredited) en la película.
Eustace Wyatt interpreta a Doctor (uncredited) en la película.
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